General Description

The All-American Canal System, located in the southeastern corner of California, consists of the Imperial Diversion Dam and Desilting Works, the 80-mile All-American Canal, the 123-mile Coachella Canal, and appurtenant structures. The system has the capacity, through water diversions from the Colorado River at Imperial Dam, to irrigate about 530,000 acres of fertile land in the Imperial Valley and about 78,530 acres in the Coachella Valley. No power is developed on the system by the Federal Government. The Imperial Irrigation district has constructed powerplants at Pilot Knob Check and Wasteway, and Drop Nos. 2, 3, and 4 of the All-American Canal. Powerplants are now (1984) under construction at Drop Nos. 1 and 5.

Plan

Irrigation water is diverted from the Colorado River at Imperial Dam through desilting basins into the All-American Canal on the California side and the Gila Gravity Main Canal on the Arizona side. These two canals and their branches carry water to their respective project areas, where the water is then delivered to the lands through distribution systems.

Unit descriptions and facilities

Imperial Dam and Desilting Works

The Imperial Dam and Desilting Works are situated on the Colorado River 18 miles northeast of Yuma, Arizona. The purpose of the dam is to raise the water surface 25 feet and provide controlled gravity flow of water into the All-American and Gila Gravity Main Canals. The desilting works remove most the sediment carried by the Colorado River. This sediment removal prevents clogging of the canals and subsequent, expensive, difficult maintenance.

To meet the irrigation diversion requirements at Imperial Dam, the flow of water in the Colorado River arriving at the dam is controlled by releases from Parker Dam, 150 miles upstream. Hoover Dam, 303 miles upstream; Davis Dam, 235 miles upstream and Glen Canyon Dam, 657 miles upstream; along with other dams, provide essential flood protection and storage. Ordinarily, the quantity of water released from these dams is coordinated with annual downstream requirements. However, during years of high runoff from the mountains, any extra water that cannot be held in allotted reservoir space is released at rates designed to minimize flooding while maintaining essential flood storage space in the reservoirs.

Senator Wash Dam, Reservoir, and Pumping-Generating Plant are located in California 2 miles upstream from Imperial Dam. Senator Wash facilities were not constructed as part of the All-American Canal System, but are an integral part of operations at Imperial Dam. Senator Wash is an offstream regulating reservoir. When the flows arriving at Imperial Dam from the Colorado River exceed diversion demands, water is pumped into the reservoir and released at a later date when demands are greater than the flow arriving at Parker Dam.

The reservoir created by Imperial Dam initially had a capacity of 85,000 acre-feet. This storage capacity was not considered a project feature and, as anticipated, the reservoir quickly filled with sediment. The reservoir capacity is now considered to be 1,000 acre-feet and intermittent dredging is required to maintain required diversion capacity at the Gila Gravity Main Canal Headworks.

Imperial Dam is a reinforced concrete structure of the monolithic slab-and-buttress type consisting of an overflow weir, canal headworks at each end of the dam, and a sluiceway located between the All-American Canal Headworks and the overflow weir. The dam is 3,472 feet long, including a 490-foot rockfill dike at the Arizona end. The overflow weir is 1,197.5 feet long and designed to pass a flow of 142,000 cubic feet per second. The overflow weir, in conjunction with the California Sluiceway, is designed to pass a maximum flood of 185,000 cubic feet per second, not including any diversions to the canal systems.

The two canal headworks are equipped with trashracks to prevent large pieces of debris from entering the canal systems. Ordinarily daily removal of the accumulation of trash is required. Trash removal is accomplished by an electrically powered rake device which pulls the trash up and dumps it into small, rail-mounted cars. The cars are moved to a chute where the trash is dumped into a truck and hauled to a disposal site where it is either burned or buried.

The design of the desilting works for the All-American and Gila Gravity Main Canals are significantly different. The Gila facility consists of a concrete-lined basin, which allows sediment to settle to the bottom while clear water is skimmed off the top as flows pass over the diversion control gates into the canal.

The All-American Canal Desilting Works are more elaborate. The flow into the canal is controlled at the headworks before the water passes through the desilting works rather than after, as at the Gila facility. The headworks consists of four roller gates, each 75 feet long and 22 feet high, including apron and flash weir. Downstream from the roller gates are four concrete channels with vertical concrete walls between the channels. Three of the channels carry water to the three existing desilting basins. The fourth channel was constructed to serve a fourth basin if found to be needed. All four channels are equipped with gates to permit water to bypass the basins through effluent channels when necessary. The three basins are separated into halves by a long tapered influent channel with the vertical slots along the sides designed to evenly distribute water entering the basin. The water crosses each basin half at a low enough velocity to allow the sediment to settle to the bottom, where it is moved by rotating scrapers to a central pedestal containing a rotating mechanism and piping system. The clear water near the surface flows over weirs, that comprise the long sides of the basins, into effluent channels leading to the All-American Canal. The pipe system under each basin half discharges the collected sediment, along with the necessary water to move it, into the California Sluiceway. The combination of water and sediment is refereed to as sludge.

The California Sluiceway extends from the 12 radial gates, located between the All-American Canal Headworks and the overflow weir, downstream about 3,000 feet. As sediment collects in the sluiceway, it is moved downstream by high rate, short duration (sluicing) flows of water discharged through the sluiceway gates. The sluicing flows usually are 8,000 cubic feet per second released for a 20-minute period, although many different flow rates, time periods, and combinations of gates are used. This procedure also removes some sediment from Imperial Dam Reservoir.

Prior to 1964, the sediment from the desilting basins found its way down the river and, as water was diverted from the Colorado River, a disproportionate amount entered the Mexican irrigation system. As a means of resolving this problem, a channel was constructed in 1964 from the end of the California Sluiceway to the reservoir area above Laguna Dam. A large settling basin was excavated about midway in this 4-mile-long channel to collect the sediment moved out of the sluiceway. Dredges pump the sediment from the settling basin to the adjacent flood plain. The first dredging operation started in 1965 and has since been intermittently required about every 2 years.

The sluicing flows from Imperial Dam are stored behind Laguna Dam and released over extended periods. Laguna Dam releases become part of the water delivered to Mexico. This procedure requires considerable fluctuation of the reservoir elevation, which limits the value of Laguna Reservoir as a recreation resource.

The California Sluiceway is also used to discharge excess water flows arriving at Imperial Dam that are not pumped to Senator Wash Reservoir or diverted to the canals. It is preferred to keep water from passing over the overflow weir to prevent damage to roads and other facilities immediately below Imperial Dam.

All-American Canal

The All-American Canal serves the Imperial and Coachella Valleys in southern California and the Yuma Project in California and Arizona. The canal has a design capacity of 15,155 cubic feet per second from the desilting works to Siphon Drop, 14.7 miles downstream. From Siphon Drop, the capacity reduces to 13,155 cubic feet per second for another 6 miles to Pilot Knob. The capacity of the canal is 10,155 cubic feet per second for the next 15.5 miles to Drop No. 1 where the Coachella Canal starts. From Drop No. 1, the canal continues west, parallel to the Mexican border for another 44 miles, gradually reducing in capacity from 7,755 to 2,655 cubic feet per second. At this point, the canal connects with the Westside Canal about 10 miles west of Calexico (about 80 miles from Imperial Dam). The design capacity of the All-American Canal includes 155 cubic feet per second for the City of San Diego, California; however, the San Diego diversion point has been changed from Imperial Dam to a point above Parker Dam.

Water is diverted from All-American Canal to most of the Reservation Division of the Yuma Project in California at four turnouts between the Laguna Dam area and Siphon Drop. A turnout at Siphon Drop diverts water to the Yuma Main Canal for the Valley Division of the Yuma Project in Arizona plus some areas of the Reservation Division.

Pilot Knob facilities include a powerplant and wasteway. Much of the water required to meet Mexican treaty requirements is diverted from the Colorado River at Imperial Dam into the All-American Canal and is returned to the Colorado river through Pilot Knob Powerplant, thus creating a significant production of electricity. Otherwise, water is delivered to Mexico through the Yuma Main Canal; from the Colorado River below Laguna Dam; and from drains, wasteway flows, and Gila River flows. The Pilot Knob Wasteway automatically discharges water from the All-American Canal when the canal elevation becomes to high.

The total length of canals and drains operated and maintained by the Imperial Irrigation District is about 3,161 miles. The distribution system was constructed by the district and consists of 1,472 miles of laterals. The drainage system consists of about 112 miles of closed drains and 1,341 miles of open drains. The district has constructed hydroelectric powerplants at Pilot Knob and Drop Nos. 2, 3, and 4 with capacities of 33,000, 10,000, 9,800, and 19,600 kilowatts, respectively.

Coachella Canal

From its turnout at Drop No. 1 on the All-American Canal, the Coachella Canal proceeds in a northwesterly direction for 123 miles. The first 49 miles, originally constructed as unlined canal, have been replaced with a concrete-lined canal. The last 37 miles of the canal are also concrete lined, which still leaves 37 miles unlined. The original unlined canal had a capacity of 2,500 cubic feet per second; the recently constructed, concrete-lined canal has a design capacity of 1,550 cubic feet per second.

As part of the Colorado River Basin Salinity Control Project (Title I, Public Law 93-320, June 24, 1974), the congress provided for lining the first 49 miles of the canal to recover most of the water lost by seepage. To maintain water deliveries during construction and avoid wet areas caused by seepage, a separate canal running nearly parallel to the original unlined section was designed. Construction of this newly relocated canal began in 1979 and was completed and put into operation in late 1980. The concrete-lined canal is estimated to save 132,000 acre-feet per year.

The Coachella Valley County Water District's distribution system, designed and constructed by the Bureau of Reclamation, is largely underground. The system consists of gravity flow concrete pipelines, with a few small pumping plants serving the higher areas. The network of laterals totals about 495 miles.

Completed in 1949, the protective floodworks along the east side of the Coachella Valley consist of two detention dikes along the canal and three wasteways to carry floodwaters impounded by the dikes to natural drainage channels, and protect the main canal and distribution system from possible storm damage. A rehabilitation and betterment program, essentially completed in 1977, added a remote control system, terminal regulating reservoir, additional flood control structures, demossing screens, and other improvements.

In 1988, Reclamation experimented with a state of the art method of lining.  Called in-place lining, a canal can be lined with polyvinyl chloride (PVC) and concrete while water is flowing in the canal.  In August of 1988, Reclamation awarded a contract to line 1.4 miles of the canal between Siphon 14 and 15.  The contract was finished in April 1991.

Operating agencies

The All-American Canal below Pilot Knob was transferred to the Imperial Irrigation District for operation and maintenance on March 1, 1947. The district assumed responsibility on May 1, 1952, for those works above Pilot Knob including the All-American Canal Headworks, desilting basins, and the first 49 miles of the Coachella Canal. On December 7, 1982, the operation and maintenance of Laguna Dam, all Senator Wash facilities, and the remainder of Imperial Dam were transferred to the district.

The lower 74 miles of the Coachella Canal and protective works were transferred to the Coachella Valley Water District on March 25, 1949, for operation and maintenance. The distribution system in the Coachella Valley was transferred to this district in 1954. On November 1, 1982, the operation and maintenance of the initial 49 miles of the Coachella Canal were transferred to the district.

Development

The Imperial Valley lies between the Mexican boundary and the Salton Sea, bounded on the east by sandhills and on the west by the foothills of the San Diego Mountains.

Coachella Valley is located in the Salton Sea Basin. It lies partly in Riverside County and partly in Imperial County, California. The valley is surrounded on all sides but the south by mountains and is about 50 miles long, 1 mile wide at the northern end, and 11 to 12 miles wide in the center. Ground water is present and before the Coachella Canal was constructed the land was irrigated with water from private wells.

In 1853, interest was aroused in the possibility of irrigating these lands from the Colorado River. The legislature of California, in 1859, asked the Congress to cede 3 millions acres to the state of California for reclamation by irrigation. The Public Lands Committee of the House of Representatives acted favorably on this application, but in 1862 the bill failed to pass. The route proposed for the canal was practically the same as that used 40 years later for the Alamo Canal.

The Colorado River Irrigation Company was formed in 1891-1892 and the entire problem of irrigating the Colorado River delta was carefully examined and important features worked out, but financial difficulties brought about failure of this company. The California Development company, formed in 1896, succeeded where the original company had failed and construction was begun in 1900.

The first project to irrigate Imperial Valley was Alamo Canal. The canal delivered water to the upper channel of the Alamo river, which flows north toward the Salton Sea in the valley center, offering suitable opportunities for developing auxiliary distribution structures. By September 1904, nearly 8,000 valley settlers were operating 700 miles of canals and irrigating 75,000 acres.

The Alamo Canal, however, was difficult to operate without upstream control of the Colorado river. The channel required almost constant dredging to control silt, and an extensive levee system was constructed for protection from flood damages. In spite of these precautions, the Colorado River, while carrying a major flood from the Gila River Basin, washed out the Alamo Canal heading in 1905. The river partially changed its course to follow the canal and the Alamo River into the Salton Sea. Water flowed into the interior for nearly 2 years and inundated some 330,000 acres. The Southern Pacific Railroad Company, alarmed about the threat to the prospering Imperial Valley and to the railroad through the basin, finally returned the Colorado river to its natural channel on February 10, 1907, and controlled diversion of irrigation water through the Alamo Canal was resumed.

Investigations

Although the feasibility of constructing a canal wholly within the United States was studied as early as 1876, a report in 1919 covered the first complete survey and cost estimate for an All-American Canal. The Congress, desiring additional information, authorized an examination which resulted in a report which recommended control of the Colorado river by a multiple-purpose reservoir project at or near Boulder Canyon, and the construction of a high-line canal, together with a diversion dam and desilting works, to carry diverted water into the Imperial Valley.

Authorization

The All-American Canal System was authorized under the Boulder Canyon Project Act of December 21, 1928 (45 Stat. 1057).

Construction

Construction of the All-American Canal began in 1934, following the construction of Hoover Dam. The first irrigation water was delivered in 1940. The construction of Imperial Dam and Desilting Works began in January 1936 and was completed in July 1938. Coachella Canal was built during the period from August 11, 1938, to June 1948. Construction was interrupted by World War II, and work stopped from 1942 to 1944. Construction of the Coachella distribution system was initiated in 1948 and completed in 1954.

Benefits

With an assured water supply, the increase in production of farm crops in the Imperial and Coachella Valleys has been phenomenal. The soils of these two valleys, combined with a favorable climate, have long been noted for production of fruits and vegetables that reach the market during the winter season when shipments from other areas are either nonexistent or at a minimum. The Nation's domestic date gardens are concentrated primarily in the Coachella Valley, with 90 percent of this country's production originating there. Other principal crops on irrigated farms are alfalfa, lettuce, cotton, carrots, citrus fruits, cantaloupes, watermelons, barley, tomatoes, sugar beets, grapes, sweet corn, and bell peppers.

Recreation

Imperial Dam forms a reservoir area with a nearly stable water surface elevation of 181 feet above sea level. Camping, hunting, picnicking, swimming, boating, and year-round fishing for bass, catfish, bluegill, and crappie are popular activities in the reservoir area.

For specific information about any of these recreation sites, click on the name below.

Imperial Reservoir Area: Mittry Lake Wildlife Area
Imperial Reservoir Area: Picacho State Recreation Area
Imperial National Wildlife Refuge

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